The present invention relates to a liquid crystal (LCD) apparatus, and more particularly to the LCD apparatus with a so-called In-Plane Switching (IPS) mode in which a transmission/shut off of the light is controlled by applying an electric field in a lateral direction to liquid crystal molecules aligned in a horizontal direction.
As a system of orienting the electric field applied onto the liquid crystal in parallel to the substrate (which is referred to as a lateral electric field system or an IPS mode), a system in which an interdigital electrode is located on one substrate has been proposed in JP-A-63-21907, JP-A-9-80424, and JP-A-2001-056476. It is known that since this system allows the liquid crystal molecules to be rotated on a substantially parallel plane to the substrates, this system may reduce the difference in the degree of the double refraction, or birefringence when the electric field is applied and when it is cut off and provide a wide viewing angle.
However, it is understood that though the IPS mode reduces the change of the birefringence of the liquid crystal itself, when an operator views the display from the oblique direction shifted from the absorption axis of the polarizer, the IPS mode brings about light leakage due to the characteristic of the polarizer itself. Another system provided with a retardation film for preventing the light leakage in the oblique direction of the polarizer has been proposed in JP-A-2001-350022. This publication basically discloses improvement of the viewing angle of only the polarizer itself in consideration of the effect of the liquid crystal about the VA mode.
Further, the Japanese Patent No.3204182 discloses means for solving color shift to white in the specific viewing directions.
Moreover, the Japanese Patent No.2982869 discloses location of the retardation film on one inside of the polarizer for improving the viewing angle characteristic of the black image.
As the other references, the following publications may be referred:
(1) Japan Society of Applied Physics, Optic Conference, “Crystal Chemical”, Chapter 5, Pages 102 to 163, issued in the fourth print of the first edition in 1984 and published by Morikita Publishing Ltd.
(2) J. Opt. Soc. Am. “Optical in Stratified and Anisotropic Media: 4×4—Matrix Formulation” D. W. BERREMAN, 1972, Volume 62, No. 4, Pages 502 to 510.
A disadvantage to be overcome by this invention is light leakage and color shift in the oblique direction in the LCD apparatus of the IPS mode for controlling transmission and cut-off of light by applying the electric field in the lateral direction onto the liquid crystal molecules aligned in the horizontal direction.
The IPS mode LCD apparatus is configured to have liquid crystal molecules aligned homogeneously in the horizontal direction and two polarizers with their absorption axes crossed at right angles in the vertical and the horizontal directions from the frontal view of the display. When an operator views the display obliquely from the vertical or the horizontal direction, the absorption axes of these polarizers are viewed to be crossed at right angles and the homogeneously aligned liquid crystal molecules are located in parallel to the absorption axis of one polarizer. These locations allow the luminance at black state to be sufficiently reduced. On the other hand, when the operator views the display obliquely at an azimuth angle of 45°, the angle formed between the absorption axes of the two polarizers is shifted from 90°. This shift thus causes the transmitted light to be double-refracted and thereby to be leaked, thereby being able to sufficiently reduce the luminance at black state. Further, the leakage quantity of light is variable depending on each wavelength, and the variety brings about the color shift.
The foregoing cited publications discuss the viewing angle characteristic only in light of the luminance characteristic and do not consider this problem about the color shift.